NASA to test potential 400Mbps laser link for Mars

NASA hopes to launch a near-infrared laser transceiver to test a system that could one day be used to communicate with astronauts on Mars.

The Deep Space Optical Communications (DSOC) experiment will head off into the void with Psyche, an asteroid-chasing probe that is scheduled to blast off on October 5. While they journey toward 16 Psyche, a metal-rich asteroid, the DSOC system will spend two years attempting to communicate via laser with two ground stations in Southern California.

NASA believes DSOC's near-infrared lasers can trounce the data transmission speeds achieved using radios.

"DSOC was designed to demonstrate 10 to 100 times the data-return capacity of state-of-the-art radio systems used in space today," enthused Abi Biswas, DSOC's project technologist working at NASA's Jet Propulsion Laboratory. "High-bandwidth laser communications for near-Earth orbit and for Moon-orbiting satellites have been proven, but deep space presents new challenges."

NASA's most recent Mars rover, Perseverance, can communicate with orbiters at two megabits per second. The Mars Reconnaissance Orbiter can chat to Earth at between 0.5 to 4 megabits per second.

Improving those speeds by a factor of between 10 and 100 with lasers therefore has an obvious benefit – even if the pesky limit that is the speed of light means it won't allow synchronous comms with the Red Planet.

DSOC uses near-infrared light, which can carry more information than radio waves, allowing ground stations to receive more data at once. Scientists would also benefit if spacecraft venturing further out into the Solar System could send more detailed images or even video captured from their cameras. 

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The DSOC transceiver uses a camera attached to a 22-cm-aperture telescope to automatically scan for and pick up a near-infrared laser uplink beamed from NASA's Optical Communication Telescope Laboratory (OCTL) in Wrightwood, California, to receive commands. It will also locate the 5.1-metre Hale Telescope at Caltech's Palomar Observatory in San Diego County, California, about 130 kilometers away from the OCTL, and transmit data to it.

The photon detector in the Hale Telescope is cryogenically cooled to dampen any noise, so it can better detect the DSOC's laser light. The time it takes to send and receive signals from the DSOC will increase over time as the Psyche spacecraft travels toward its target asteroid. 

The maximum distance that the DSOC experiment will be expected to cover is over 300 million kilometers.

To better ensure the laser transceiver can pick up the uplink signal, engineers have fitted the Psyche spacecraft with special struts that hold its telescope in place, preventing it from being affected by vibrations.

"Every component of DSOC exhibits new technology – from the high-power uplink lasers to the pointing system on the transceiver's telescope and down to the exquisitely sensitive detectors that can count the single photons as they arrive," explained Bill Klipstein, the DSOC project manager at JPL. "The team even needed to develop new signal-processing techniques to squeeze information out of such weak signals transmitted over vast distances." ®